Solids drying process



July 7, 1970 E. S. JOHANSON 125 uon-connsuslms couosusmmn AND 21 summon20 1a 1 r I -17 GRINDINGAND 1 name srem SLURRY0lL36/ HEATER 19 1 I I 30REACTOR38 28 Z VENTGASES40 3 v HEDIUMSIZEJ 34 7 SOLID PRODUCTS 44C0AL10* swam TANK 32 IEATED/ V was ;AS12

INVENTORI EDWIN S. JOHANSON AGENT United States Patent 3,518,773 SOLIDSDRYING PROCESS Edwin S. Johanson, Princeton, N.J., assignor toHydrocarbon Research, Inc., New York, N.Y., a corporation of New JerseyFiled Feb. 29, 1968, Ser. No. 709,468 Int. Cl. F27b 5/00 U.S. Cl. 34-269 Claims ABSTRACT OF THE DISCLOSURE A process for removing moisture froma fine particulate solid material by contacting a drying gas with theparticulate material. The use of a readily condensible gas for thedrying gas is disclosed with subsequent condensing of the gas after thecontacting step, whereby the fines contained in said gas may berecovered from the condensate.

BACKGROUND OF THE INVENTION This invention pertains to the field ofmoisture removal from particulate solids. More specifically, it relatesto the drying of carbonaceous material such as, coal, lignite or peatprior to its introduction into a coal conversion process for thepurposes of making hydrocarbon products from the coal.

Typically, the coal conversion processes which are known to the artrequire the pulverizing and drying of the coal, followed usually, by aslurrying of the pulverized coal into a hydrocarbon liquid and thensubjecting said slurry to a hydrocracking and/or hydrogenation. Bothcatalytic and noncatalytic processes are known in the art.

Examples of such processes are described in the Johanson U.S. Pat. Re.25,770 and the Schuman et a1. patent,

U.S. Pat. No. 3,321,393. In this type of process, the dried, pulverizedcoal is slurried with an oil from the process and is then passedupwardly with hydrogen through a catalytic bed at such velocity wherebythe bed exists in an expanded or ebullated state. A major requirement ofsuch processes is that the coal be substantially free of moisture, sincesuch moisture results in excessive foaming in the slurry preparationstep and reduction of the hydrogen partial pressure in the reactionzone.

The usual methods for drying the coal, incorporate the use of a dryinggas which is contacted with the particulate coal either during or afterthe pulverizing step. A major problem in such a drying step is theexcessive retention of fines in the drying gas after the contactingprocess. The fines present a problem for two reasons: First, theyrepresent a substantial loss in feed material and can prove to be ratherexpensive from a yield point of view; second, there has been increasingattention drawn to the problem of air pollution in this country today,and the venting of a carbonaceous fines-containing gas to the atmosphereis detrimental to such a situation. Many jurisdictions now havestatutory prohibition against introducing such contaminated gases to theatmosphere.

In the past, the drying processes have incorporated filter bags andseparation devices of that nature to remove the,

fines from the drying gas, however, such devices have proven to be quiteexpensive and inefiicient, especially with fines in the 1-5 micron sizerange. The use of cyclones and devices operating on the centrifugalforce principle has been attempted, however, it has been found that thefines particles are too small to be effectively separated by suchdevices.

SUMMARY OF THE INVENTION I have discovered a method by which fines maybe effectively removed from gases that have been contacted withparticulate solids for drying purposes and, which also renders the finesamenable to subsequent downstream processing. My invention isparticularly useful with respect to known methods of separation offines, since it allows one to efficiently utilize a centrifugal forcedevice to separate the fines from the drying gas.

I have found that by using an inert, readily-condensable gas as thedrying gas, I can accomplish the desired moisture removal from theparticulate material and subsequent to such moisture removal, subjectthe gas to condensation conditions whereby the fines are retained in thecondensate and are readily removable therefrom.

The separation methods used may be any of those known in the art, e.g.,simple settling devices, evaporators, etc. More particularly, however,my invention is specifically useful with a centrifugal force typedevice, such as a cyclone. In such a case, the condensation conditionsmay easily be adjusted such that nuclear condensation is effected,whereby the readily condensable gas liquefies in a mist or foglikemanner. The fines in the gas act as nucleating sites for the mistparticles and these nucleated mist particles then have sufficient weightto be centrifuged from the noncondensed gas.

It is a further object of my invention to use readily condensablematerials, such as hydrocarbons which are compatible with the coalconversion process, whereby the fines-containing condensate may bedirectly introduced to the conversion reaction zone without additionalintermediate separation steps.

Thus, by use of my invention, one may recover a substantial amount offeed material which would normally be lost from the process and, at thesame time, avoid producing an air-contaminating waste.

DESCRIPTION OF THE DRAWING The drawing is a schematic flow diagram of acoal grinding and drying process incorporated in a coal conversionprocess.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, coal at10 having a size in the range of about 1%" diameter, is introduced alongwith a drying gas at 12 to a grinding and drying zone 14. The drying gasconsists of a readily-condensible inert gas which has been heated inheater 19 to a temperature sufficient to remove moisture from thepulverized coal. Temperatures within the range of about 200 F. to about600 F. are normal for such an operation. By inert, it is meant that thegas does not react in any way with the carbonaceous material except forsupplying the heat and carrying medium for removing the moisturetherefrom. The designation readily-condensible is meant to include allthose gases which have boiling points which would allow them to beliquefied within the reasonable temperature parameters of a dryingprocess of this nature. It would be expected, for instance, thatmaterials which had boiling points within the range of above F.preferably at least ambient temperatures to perhaps, about 300 F. wouldbe suitable. One would not, for example, think of oxygen, nitrogen orcarbon dioxide as being suitable for this process, as they are notconsidered to be readilycondensable. Gases, on the other hand, such assuperheated steam and hydrocarbon materials, both aliphatic andaromatic, boiling within the range from about 100 F. to about 300 F, canbe used for this process.

The grinding and drying step may be carried out simultaneously or thecoal feed may be ground separately and then dried. There are a number ofcontacting processes known to the art which can be utilized in step 14,e.g., a fluidized bed.

The moisture and fines-containing gas is removed overhead through line16 to enter a cyclonic step 17 that separates from the vapors, thereadily removed, medium sized solids which pass directly through line 30to the slurry preparation system 32. A portion of the vapors from step17, equal in quantity to the drying gas, passes through line 18 to bereheated in heater 19. The balance of the vapors, which contain themoisture removed from the coal, are removed through line 21 tocondensation and separation step 20.

A particular advantage of my invention is that the amount of vaporremoved to the condensation step from the cyclone 17 is only thatrequired to carry the total moisture removed from the coal. The majorportion of the drying gas is reheated and recirculated. Thus, there isno drying gas exited from the process. In practice, of course, smallmake up portions would be required from time to time.

The condensation of the readily-condensable gas may be effected simplyby reducing the temperature of the vapor in line 21 to a sufiicientlevel to liquefy the gas. One method of accomplishing this temperaturereduction is by shunting a portion of a cooled gas such as thenoncondensable in line 22 through line 25 into line 21. This type ofcooling is particularly effective in that it will favor mist formationthrough the vapors rather than condensation on the conduit andseparation zone surfaces. Other methods of cooling would include wateror hydrocarbon liquid injection.

The separation step may be effected by gravity means or, if desired, canincorporate a centrifugal force type device, such as cyclones, orcentrifuges in which case, a net water efiluent, free from fines, isremoved in line 23. The condensate and the fines are removed throughline 24. If the drying gas is a linear or cyclic aliphatic hydrocarbonor an aromatic hydrocarbon, i.e., compatible with those materials in thereaction zone, the condensate and fines may be introduced to the slurrytank 32 through line 28. In slurry tank 32, a slurry of the driedpulverized coal from line and slurry oil in line 36, is prepared. Themixture then proceeds to the reaction zone 38 wherein the coal isconverted to products which are removed in line 44; slurry oil which isremoved in line 36 and recycled to the slurry tank; and vent gases inline 40. As mentioned above, the vent gases may be used as the dryinggas in the grinding and drying step.

If it is desired to introduce the condensate into the reaction zone, itis necessary that the water which it contains be removed prior to suchintroduction. The removal of the water may be effected by normalfractionation methods. It is preferable, of course, that thecondensation step be operated at a condition whereby the water will beremoved through line 22 with the noncondensable gases or as liquid freeof fines through line 23. The removal of the water as a vapor wouldessentially limit the minimum temperature of the step to about 212 F. Ifsuch temperature requirements are not feasible, however, there arenumerous methods known to the art whereby water may be removed from thenonaqueous liquid condensate.

When steam is the drying gas, it is heated to about 500 F. andapproximately ten pounds of steam per pound of water to be removed fromthe solids is used. As described above, the steam is contacted with thecoal at a temperature of about 240 F. The gas issuing from the dryingzone is now 11 parts steam vapor and after cyclone step 17, it is splitinto ten parts which are recirculated through the heater 19 and one partwhich is introduced to condensation and separation step 20 wherein someor all of the steam is condensed by indirect heat exchange or by directintroduction of a quench medium, e.g., condensed water or gas as in line25.

As previously mentioned, an organic material such as a linear oraliphatic hydrocarbon or aromatic hydrocarbon may be used as the dryinggas. An example of this mode of operation is the use of a gas composedof 82 percent by weight of a hydrocarbon having a boiling point of about275 F. and 18 percent by weight Water vapor.

Thus, for the removal of one pound of water, the drying gas contains 7.6pounds of hydrocarbon and 1.6 pounds of water vapor. The gas exitingfrom the drying step, i.e., cyclone 17, contains 7.6 pounds ofhydrocarbon and 2.6 pounds of water vapor. To shunt the one pound ofremoved water to the condensation step 20, a total of 3.9 pounds of gasis removed in line 21, said gas containing 2.9 pounds of hydrocarbon.The remaining 4.7 pounds of hydrocarbon and 1.6 pounds of water would berecirculated to heater 19. The gas in line 21 is cooled to about 200 F.using the heretofore described methods. The water contained in thisstream will not condense due to its reduced partial pressure, whereasabout /3 or about 0.9 pound of the hydrocarbon condenses on the nucleusof the coal fines. Thus, with a carryover of fine solids of about tenweight percent of the water vaporized, the concentration of solids inthe condensate is about eleven weight percent. The condensate and finesare then separated and removed through line 24 and introduced to theslurry tank through line 28.

The uncondensed water vapor with some gaseous hydrocarbon at 200 F. inline 22 is further cooled and condensed. It is a relatively simpleoperation to separate the immiscible hydrocarbons and water. Theseparated hydrocarbons are then either reused for makeup in the dryinggas or added to the slurry.

Obviously, many modifications and variations of the invention ashereinabove set forth may be made without departing from the spirit andscope thereof, and therefore, only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. In a process for removing moisture from a particulate carbonaceousmaterial of the type wherein a hot, inert drying gas is contacted withthe particulate material and wherein after the contacting step, the gascontains moisture and fines consisting essentially of the carbonaceousmaterial, the improvement which comprises using a readily-condensablegas selected from the group consisting of superheated steam and linearand cyclic aliphatic and aromatic hydrocarbons having a boiling rangefrom about to about 300 F. as the inert gas and condensing said gasafter the contacting step whereby the fines may be recovered with thecondensate.

2. The process as claimed in claim 1 wherein the carbonaceous materialis coal which is being dried for subsequent conversion to liquid andgaseous products in a hydrogenation zone.

3. The process as claimed in claim 2 wherein the drying gas contains anorganic material selected from the group consisting of aliphatic andaromatic hydrocarbons boiling within the range from about F. to about300 F. or combinations thereof.

4. The process as claimed in claim 3 wherein a substantial amount of theorganic material contained in the drying gas is condensed after thecontacting step without condensing the water vapor contained therein andwherein the fines-containing condensate is introduced to thehydrogenation zone.

5. The process as claimed in claim 4 wherein the drying gas contains ahydrocarbon material having a boiling point of about 275 F. and whereinthe drying gas is cooled to a temperature of about 200 F., whereby saidhydrocarbon material condenses without condensation of any water vaporcontained in the drying gas.

6. The process as claimed in claim 2 wherein the drying gas issuperheated steam.

7. The process as claimed in claim 6 which further includes the stepsof:

(a) heating the steam to about 500 F. prior to the contacting step andthen;

(b) contacting the steam with the solid at a rate of about ten pounds ofsteam per pound of water to be 5 removed from the solid and at atemperature of about 240 F. and then;

(c) exiting the steam from the contacting step and then;

(d) splitting the steam into a major portion equal to the amount ofsteam originally entering the contacting step and a minor portion equalto the amount of water removed from the solid and then;

(e) recirculating the major portion to the heating step and;

(f) condensing all or part of the minor portion.

8. The process as claimed in claim 2 wherein the drying gas is condensedby introducing a cooling material selected from the group consisting ofwater, steam,

whereby the condensate liquefies as mist-like droplets, said dropletsbeing nucleated by the fines contained in the gas.

9. The process as claimed in claim 8 wherein the nucleated droplets areremoved from the gas 'by centrifugation.

References Cited UNITED STATES PATENTS 2,843,942 7/1958 Whitsel 3436 XRJOHN J. CAMBY, Primary Examiner US. Cl. X.R.

and liquid and gaseous hydrocarbons to the drying gas 15 3436

